Elastane yarns are synthetic filament yarns which are produced as mono- or multifilaments—dependent on the intended use—within the linear density range from 11 to 2500 dtex (cf. F. Fourne: Chemiefasern/Textilindustrie 44/96; June 1994, page 392). Higher linear densities, which extend more or less into the typical application range of natural rubber yarns, are perfectly interesting, however, for example for use as elastic undertapes for upholstery fabrics or as leg border for underwear and swimwear articles and also for the medical and technical sector.
However, the need to evaporate the spinning solution solvent in the spinning chimney imposes technical limits on producing coarse elastane linear densities by the dry spinning process. Owing to the high linear density of 2500 dtex or more and the small yarn surface area of coarse linear densities, it is very difficult to evaporate sufficient spinning solution solvent in order that the yarn may be drawn off without sticking together. Droplets of the spinning solution solvent still present at the down-stream end of the spinning chimney lead to stuck-together filaments which, after winding onto bobbins, are no longer satisfactorily processible off the bobbins. Furthermore, without incurring reduced spinning efficiency due to a reduction in the spinning speed, it is very difficult to lower the residual solvent content in the elastane yarn to a minimum without further cost-intensive steps, such as washing or steaming of the yarn.
By using a lower spinning speed it is possible to increase the residence time in the dry spinning chimney and to reduce the residual level of, for example, dimethyl-acetamide (DMAC) solvent. However, this is at the expense of the spinning efficiency. Nor is it possible to raise the temperature in the spinning chimney to beyond a certain level, since this may give rise not only to discolourations but also to softening and melting of the yarn. The softening range of elastane yarn varies with the polymer composition, but is typically 180-230° C., and the melting range is about 250-270° C.
For this reason, in the field of the dry spinning of elastane yarn, yarn having a final linear density of above 2500 dtex has not been disclosed before. A fineness of up to 3240 dtex has been reported by Globe Manufacturing Comp. for elastane yarn reactively spun by the chemical spinning process, and a linear density of up to 2464 dtex has been reported by Fujibo Spandex for elastane yarn produced by wet spinning. Compare P. A. Koch: Faserstoff-Tabellen in Chemiefasern/Textilindustrie, February 1979, page 100.
In order that elastane yarn may be further processible, for example in ribbon weaving, they must have a certain minimum strength. A tenacity of at least about 0.4-0.5 cN/dtex is required in the case of coarse linear densities to meet these demands.
However, in the case of elastane yarn having a coarse linear density of greater than 2500 dtex it is very difficult to achieve adequate strength, since the higher level of residual solvents, for example dimethylacetamide, which act as plasticizer between the polymer chains, markedly reduce the yarn's strength.
It is an object of this invention to develop elastane yarn and a process for its production which meet the abovementioned requirements and more particularly to provide a high final linear density elastane yarn which has a low residual solvent content, high strength and high residual extensibility.